Dehydroquinate pathway biosynthesis

The biosynthesis of H4MPT can be viewed as being composed of two converging pathways, one beginning with GTP to generate the pterin portion and the other beginning with 3-dehydroquinate (DHQ) producing... 

Further information was gleaned from feeding [l- C]glucose. ° This compound was found to label only C-1 and C-10 of the C7N unit, a labelling pattern which is similar to that observed in shikimic acid (191) formed from [1- C]glucose. Neither shikimic acid, however, nor the labelled aromatic amino-acids tested were found to be precursors for the C7N unit of rifamycin S. This does not, of course, exclude earlier intermediates on the shikimate pathway and it was suggested that 3-dehydroquinate (189) or 3-dehydroshikimate (192) may be the key intermediate in the biosynthesis of this unit in rifamycin S (193). 

The w-CyN unit described was shown to be incorporated in the biosynthesis of both the ansamycins and also other related antibiotics, such as pactamycin and other compounds [188-190]. With respect to other naturally occurring compounds which contain a partial structure derived from the m-CyN unit in the molecule, asukamycin [191] is a possible shunt metabolite from 3-dehydroquinic acid in the shikimate pathway. Incorporation of [l - 3C]-AHBA (118) into the C-6 methyl group of porfiromycin (120) (a mitomycin group antibiotic) was reported (Fig. 6) [192], and the participation of a m-CyN unit in this biosynthetic pathway and the antibiotics containing a m-CyN unit were reviewed [178,188,190]. 

Quinic acid, known to be widely distributed in plants, has to be considered as a possible intermediate in aromatic biosynthesis. It has been reported to exhibit a low-order growth activity for a Neurospora mutant (S06). Secondary mutants of Aercbactor that responded well to dehydroquinic acid also responded equally well to quinic acid ( 07). E. coli mutants that utilized dehydroquinic acid, on the contrary, did not respond to quinic acid. In addition no Aerabactor auxotroph block between quinic acid and dehydroquinic could be found. In view of this and the enzymic evidence presented below, quinic acid is considered not to be on the direct pathway of aromatic biosynthesis. 

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